<!DOCTYPE html>
<html>

<head lang="en">
    <meta charset="UTF-8">
    <title>aags</title>
    <style>
        .box1 {
            width: 300px;
            height: 300px;
            padding: 100px;
            margin: 100px;
            position: relative;
            border: 100px solid #000;
            background-color: pink;
        }
        
        .box2 {
            width: 100px;
            height: 100px;
            background-color: red;
            /*position: absolute;*/
            /*left: 10px;*/
            /*top: 10px;*/
        }
    </style>
</head>

<body>
    <div class="box1">
        <div class="box2" style="left: 10px"></div>
    </div>

    <script>
        var box2 = document.getElementsByClassName("box2")[0];

        //offsetTop和offsetLeft
        console.log(box2.offsetLeft); //100
        console.log(box2.style.left); //10px
    </script>

</body>

</html>